1. Field of the Invention
Embodiments of the invention generally relate to a processing pad assembly for electrochemical mechanical processing.
2. Description of the Related Art
Electrochemical Mechanical Processing (ECMP) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion as compared to conventional Chemical Mechanical Polishing (CMP) processes. With revising the polarity of the bias, ECMP systems may generally be adapted for deposition of conductive material on the substrate. Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. The bias may be applied to the substrate surface by a conductive contact disposed on or through a polishing material upon which the substrate is processed. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the polishing material that enhances the removal of the conductive material from the substrate.
Copper is one material that may be polished using electrochemical mechanical polishing. Typically, copper is polished utilizing a two-step process. In the first step, the bulk of the copper is removed, typically leaving some copper residue on the substrate's surface. The copper residue is then removed in a second step, typically referred to as an over-polishing step.
However, the removal of copper residue may result in dishing of copper features below the plane of a surrounding material, typically a dielectric or other barrier layer. The amount of dishing typically is related to polishing chemistries and processing parameters utilized in the over polish step, along with the width of the copper features subjected to polishing. As the copper layer does not have a uniform thickness across the substrate, it is difficult to remove all the copper residue without causing dishing over some features and not removing all of the copper residue over others.
Thus, there is a need for an improved apparatus for electrochemical mechanical polishing.